1. Field of the Invention
This invention pertains generally to the field of mechanical locking devices of the type having a rod normally locked against axial movement through a lock housing by a clutch spring of reduced diameter, where the rod is released by partially unwinding the spring.
2. State of the Prior Art
The device of this invention pertains to a class of mechanical locks which generally have a rod axially movable through a lock housing, one or more coil springs tightly wound about the rod and axially fixed to the housing so as to normally grip the rod against movement through the housing. A release is provided for partially unwinding the coil spring or springs such that the internal diameter of the spring is increased and the rod is released for axial movement relative to the lock housing. Linear locks of this type have been in widespread use, particularly in recliner seats used in automobiles and other vehicles. In such installations, the housing of the mechanical lock is attached to one of the reclinable backrest or the stationary seat, while the end of the rod is connected to the other of those two seat components. In its normally locked condition the device fixes the position of the backrest. If the occupant desires to reposition the backrest, the lock is manually released, which frees the rod and allows movement of the backrest. The mechanical lock typically has a heavier exterior coil spring which returns the rod to an extended condition when the lock is released. For example, the spring may serve to bring the seat backrest to a fully upright condition. One relatively early example of such a lock is disclosed in U.S. Pat. No. 3,874,480 issued to Porter et al. and owned by the Assignee of this patent application.
In applications where bi-directional loading of the rod is anticipated, two springs may be provided, one on each side of a common release lever and axially contained between two end bushings, each bushing engaging an end tang of a corresponding spring to fix the tang and the outer end coils of the spring against rotation about the rod. The inner end coils of the springs are connected to a release lever, actuatable for simultaneously unwinding both springs to free the rod for axial movement through the housing.
The bushings serve three distinct functions. An axial bore in each bushing defines a radial bearing surface which supports the rod for sliding movement through the lock housing. A radial slot in the bushing receives an end tang of the spring, to circumferentially fix the outer end of the spring and prevent this end of the spring from turning about the rod. Finally, an axial bearing surface on the bushing is circumferentially spaced by 90 degrees from the spring tang. When the spring is pulled with the rod against the axial bearing surface by a load acting on the rod relative to the lock housing, the end coils of the spring are canted relative to the rod axis. This canting deforms the coils from a normal circular shape to an ellipsoid shape, and substantially increases the frictional engagement between the spring coils and the rod. The clutch spring better resists the load and makes for a more positive lock of the rod relative to the housing so long as the loading condition persists.
Prior art locks also feature a tubular sleeve which closely envelops the spring or springs, to prevent the coils from unwinding preferentially at the release lever while the coils at the opposite end remain in a rod gripping condition. The sleeve prevents this result by distributing the unwinding action more evenly along the length of the spring so that all coils release the rod at substantially the same time, for positive, quick release action of the lock.
Early locks of this type were housed in a cylindrical tube open at one or both ends. The clutch spring was mounted on the rod, and other components such as end bushings, actuator levers, etc. all were assembled onto the rod and then inserted into the housing. The housing wall was then swaged or welded to hold the internal components in axially fixed position within the housing. The relative positions of the lock elements in the housing is rather critical and a high degree of precision must be maintained in assembling the lock. A tube type housing makes this objective difficult to achieve with consistency.
More recently, the tube style housing has evolved into a two-piece clam shell housing, described in European patent application number 85201888.6 filed Nov. 18, 1985, Publication number 0 182 440 83. An envelope or housing is formed by two half-shells. The rod is first fitted with the two coil springs, a release lever including a containment sleeve about the springs, and a pair of end bushings which engage the ends of the coil spring. The half-shells are mated to each other with the rod assembly in-between, and welded to the bushings to form an enclosure about the rod. The axial spacing between the bushings is fixed by this welding, with springs axially contained between the bushings. The rod slides through the bushings and the housing when the spring is unwound to permit such movement.
The need to weld bushings to a lock housing has been a source of difficulty in prior art locks. In practice, it is very difficult to produce locks with welded bushings which are perfectly aligned with the rod axis, and such misalignment introduces a degree of frictional drag into the lock mechanism. In addition, the bushings add significantly to the cost of the lock, and may have to be differentially hardened to provide hard bearing surfaces as well as untreated portions which can be welded.
U.S. Pat. No. 5,157,826, commonly owned with this application, describes a method for making a linear mechanical lock in which the number of component parts is reduced by fabricating the lock housing from a single sheet of metal and embossing various elements, which previously constituted separate parts, into the single sheet. In particular, the interior dimension of the housing is such as to closely encompass the clutch springs to promote even unwinding of the spring along its length upon actuation of the lock release without a separate containment sleeve. While this prior invention represents a substantial contribution to the state of art, further improvements have been made which facilitate fabrication and assembly of the linear lock while at the same time improving the precision of the lock assembly for smoother, easier and faster lock operation.